This invention relates to an apparatus which is incorporated in a carding machine and which includes, between the doffer and the licker-in, cover elements underneath the main carding cylinder. Between the cover elements at least one discharge opening is provided through which trash and dust, separated from the fiber material, is introduced into a suction chamber.
In practice, on the cylinder clothing above the doffer fiber material is present which contains long (useful) and short fibers. Short fibers are undesired because they adversely affect the strength, particularly of fine yarns such as ring yarns. The doffer removes the preponderant portion of the fiber material from the main carding cylinder by means of its long clothing teeth. It is a disadvantage that in the doffed fiber material a substantial proportion of short fiber is present.
The main carding cylinder has a high circumferential velocity (in excess of 15 m/sec) and entrains a substantial quantity of air on its surface. This results in a vacuum at the carding cylinder in the circumferential region between the stationary cylinder cover and the rapidly moving cylinder clothing. The fibers are, on the other hand, retained and advanced by the teeth of the cylinder clothing and, on the other hand, held back by the above-noted vacuum on the cylinder surface. The fiber material is opened up to the individual fibers. In a known apparatus, as described in German patent document No. 39 02 202, to which corresponds U.S. Pat. No. 5,095,584, in the cover elements, between the doffer and the licker-in, openings are provided through which dust and, by centrifugal forces, heavy waste particles are separated. The lighter, short fibers, however, remain adhered to the cylinder clothing, particularly under the effect of the clothing teeth and the vacuum in the clothing.
It is an object of the invention to provide an apparatus of the above-outlined type from which the discussed disadvantages are eliminated and which, in particular, makes possible a substantial reduction in the short fiber proportion of the fiber removed from the cylinder by the doffer and thus permits the manufacture of a stronger yarn.
These objects and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the carding machine includes a main carding cylinder having a cylinder surface carrying a cylinder clothing thereon; a licker-in cooperating with the carding cylinder for transferring fiber material, including long and short fibers, from the licker-in to the carding cylinder; a doffer cooperating with the carding cylinder for transferring fiber material from the carding cylinder to the doffer; a cylinder cover extending circumferentially underneath the carding cylinder between the licker-in and the doffer; a force-exerting arrangement for applying, to the short fibers, a removing force greater than a retaining force exerted on the short fibers by the cylinder clothing carrying the fiber material; a waste outlet opening provided in the cylinder cover for discharging short fibers from the fiber material carried by the cylinder clothing; a suction hood coupled to the waste outlet opening for receiving the short fibers from the waste outlet opening.
By virtue of the measures according to the invention, on the teeth of the doffer clothing preferably the longer fibers remain attached so that the fiber material which remains on the cylinder clothing after contact with the dofferxe2x80x94that is, the fiber material which is not doffedxe2x80x94has a significantly higher short fiber proportion. The short fibers which at that location are opened into individual fibers and are as such situated on the cylinder clothing, are retained by the teeth of the cylinder clothing. By virtue of the fact that the separating force exerted on the short fibers is greater than the retaining force of the cylinder clothing, the short fibers are substantially entirely removed by suction. As a result, undesired short fibers are not introducedxe2x80x94as the cylinder continues to rotatexe2x80x94in the new fiber material advanced by the licker-in to the carding cylinder and thus do not arrive to the doffer. The totality of the good (long) fibers processed in the carding machine is thus to a significant measure freed from short fibers.